FRIDAY, March 10, 2017 (HealthDay News) — Yet more evidence of a link between poor sleep and excess weight: A new study finds that people who are genetically prone to obesity are more likely to be overweight if they have unusual sleep habits.

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“These data show that in people with high genetic risk for obesity, sleeping for too short or too long a time, napping during the day, and shift work appears to have a fairly substantial adverse influence on body weight,” said researcher Dr. Jason Gill of the University of Glasgow, Scotland.

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Gill, who is with the university’s Institute of Cardiovascular and Medical Sciences, and colleagues looked at statistics on nearly 120,000 people in the United Kingdom.

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The investigators said they found that sleeping fewer than 7 hours a night or more than 9 hours a night boosts the risk of obesity among those who are especially prone to it because of their genes.

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Among those with a genetic propensity toward obesity, those who slept more than 9 hours a night were almost 9 pounds heavier than similar people who slept 7 to 9 hours. Meanwhile, those who slept less than 7 hours were a little more than 4 pounds heavier than their better-rested peers, the findings showed.

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Although the study doesn’t establish a direct cause-and-effect relationship, the researchers found this effect persisted regardless of diet, health problems or income level.